This invention relates to a supporting arrangement for an outboard drive unit and more particularly to an improved resilient support for such a unit.
As is well known, it is common practice to mount outboard drive units on the hull of a water craft. In arrangements of this type, it is desirable to provide some form of resiliency in the mounting so that vibrations from the propeller and/or engine will not be transmitted back to the hull. However, if a resilient supporting structure is employed that is sufficiently flexible so as to accommodate low speed vibrations, too much resiliency may be introduced into the system and there will be insufficient damping under high speed running or when sudden changes in direction are made. Therefore, it has been the practice to employ relatively rigid shock absorbers between the propelling unit and the hull so as to achieve damping and reduce the transmission of vibrations under high speeds or when rapid changes in direction are made. Thus, previously proposed systems have not provided adequate softness under low speed running conditions. In addition to the wide range in magnitude of vibrations which must be absorbed in outboard propelling units, the vibrations occur in different directions. Vibrations in one direction may require significantly different damping than the vibrations which occur in other directions.
It is, therefore, a principal object of this invention to provide a supporting structure for an outboard propelling unit that is effective throughout a wide speed and load range.
It is a further object of the invention to provide a propelling unit suspension system that offers relatively soft characteristics under some conditions and yet will provide resiliency damping under significantly different conditions.
In conjunction with the provision of resilient mounting arrangements for outboard drive units, it has been proposed to use an elastomeric arrangement wherein an elastomer element is bonded to metal fixtures that are in turn affixed relative to the hull and the propelling unit. It is essential that the bonding between the elastomer and metal be extremely reliable to insure against failure in use. However, in order to achieve this bonding, a high degree of quality control must be insured which adds to the cost of the supporting structure.
There has been proposed an arrangement wherein an elastomeric sleeve is closely fitted and clamped within the inner and outer metal sleeves so as to avoid the necessity of a bonding arrangement. Such an arrangement is shown in Japanese utility model application No. 48-11550. With such arrangements, however, it is necessary to provide high compressive loads which result in the provision of a relatively rigid, even though elastic, support. Hence, such arrangements as heretofore proposed have not provided any significant damping for low speed vibrations.
It is, therefore, a further object of this invention to provide an improved supporting structure for outboard propelling units that may be made at a lower cost and yet will be effective throughout wide speed and load ranges.